1. Technical Field
The present invention relates generally to semiconductor fabrication equipment and in particular to a chuck used to secure semiconductor wafers. Still more particularly, the present invention relates to an electrostatic chuck used to secure semiconductor wafers.
2. Description of the Related Art
In the manufacturing process of electronic devices such as semiconductor devices based on silicon wafers, liquid crystal display panels and the like that various processing steps such as etching, ion-implantation and the like are conducted under dry conditions since high productivity by automatization can be obtained by these dry processes easily as compared with traditional wet processes. One characteristic in these dry processes is that the treatment of the articles is performed in an atmosphere of high vacuum. Further, devices having a larger and larger size and finer and finer patterning with precision for an increased density of circuit integration are required in the modern electronic industry.
Needless to say, the material under processing, e.g., semiconductor silicon wafers, glass substrate plates and the like, in such a processing treatment must be held or transported by some chucking means. One of the conventional chucking devices used for such a purpose is a vacuum chuck using a chucking plate having perforations and connected to an evacuation means so as to attract the work piece by sucking action. In principle, such a vacuum chuck cannot be used in a vacuum atmosphere because of the absence of any pressure difference between the surfaces of the work piece. Even as a chucking means used under normal pressure, vacuum chucks have a problem that the attractive force by suction is localized on and around the perforations in the chucking plate so that a local strain is caused in the work piece under working chucked thereby resulting in a decreased accuracy of alignment of the work piece for processing. Accordingly, vacuum chucks are considered to be unsuitable for use in the manufacturing process of electronic devices due to this serious problem.
Electrostatic chucks are used for holding a workpiece in various application ranging from holding a sheet of paper in a computer graphics plotter to holding a semiconductor wafer within a semiconductor processing system. Although electrostatic chucks vary in design, they all are based on the principal of applying voltage to one or more electrodes in the chuck so as to induce opposite polarity charges in the workpiece and electrodes, respectively. The electrostatic attractive force between the opposite charges presses the workpiece against the chuck, thereby retaining the workpiece.
In semiconductor wafer processing equipment, electrostatic chucks are used for clamping wafers to a support pedestal during processing. The support pedestal may form an electrode as well as a heat sink or source. Such support pedestals are used in etching processes as well as chemical vapor deposition (CVD) or physical vapor deposition (PVD) applications.
More specifically, the electrostatic chuck contains a chuck body formed of a layer of dielectric material covering a conductive pedestal base. In a unipolar or monopolar electrostatic chuck, a voltage is applied to the conductive reference. The wafer is retained by coulomb force between charge accumulated on the underside of the wafer and the voltage applied to the pedestal base.
Typically, these electrostatic chucks are manufactured by adhering an insulating layer on a metal layer. This process is time consuming and is repeated when the insulating layer wears off during processing of semiconductor devices. Therefore, it would be advantageous to have an improved method for manufacturing electrostatic chucks.